Photovoltaic solar panels, also referred to simply as solar panels, are generally of two basic designs. One design employs crystalline silicon wafers connected together and embedded in a laminating film. The laminating film and the wafers embedded therein are typically sandwiched between two panels of glass, a polymeric material or other suitable materials.
The second solar panel design employs a semiconducting material, such as amorphous silicon, cadmium-telluride (Cd—Te) or copper-indium-gallium-diselenide, (commonly referred to as “CIGS”), which is deposited on a substrate in a thin film. These thin film photovoltaic materials are typically deposited on a glass substrate by a method such as sputtering, plasma vapor deposition or chemical vapor deposition. The individual photocells are typically formed by a laser etching process, and are connected together by suitable circuitry. To complete the construction, an adhesive is applied over the photovoltaic material and associated circuitry, and a backing material is applied. The backing material is typically glass, but may be metal, a composite or a plastic material.
Solar panels are used outdoors, and so are exposed to the elements, including wind, water and sunlight. Water penetration into solar panels has been a long-standing problem. Thus, various attempts have been made to reduce the water vapor transmission rate of the solar panel (WVTR). Solar panels may also be deleteriously affected by wind and sunlight, which may result in failure of the adhesive layer. Wind causes obvious physical damage, and sunlight results in heating of the solar panel and exposure to ultraviolet (UV) radiation.
Operating temperatures of solar panels have been measured as high as 110 C. Thermoplastic adhesives soften at elevated temperatures, causing creep in the panel, and are susceptible to UV-induced breakdown. Many thermosetting materials suffer from unacceptably high WVTR.
One presently used adhesive is ethylene vinyl acetate (EVA). The EVA is applied to the solar panel, generally including a peroxide which can crosslink the EVA. The EVA is then cured in place on the solar panel. Crosslinked EVA provides high strength, but suffers from a relatively high WVTR.